1. Field of the Invention
This invention relates to a tethered aircraft, specifically to a tethered aircraft having a remotely-controlled angle-of-attack.
2. Description of the Prior Art
A kite pulls hard when it flys low. When it flys low its angle-of-attack is large. When it flys high its pull is much less and its angle-of-attack is small. To make it fly high the string is fastened higher up on the kite. To make it fly low the string is fastened lower down on the kite.
The point to which the string is fastened is the towing-point. The towing-point is usually chosen by trial to produce flight at maximum altitude, but for greatest pull the towing-point is set to provide flight at lower altitudes.
When the string, the tether, is constant in length kites fly stock-still in midair in steady wind, and so, historically, kites were useful for lifting objects; photographic cameras, weather instrumentation, and before powered flight the lifting of people. Kites were used to tow wagons and boats. To tow these heavy objects low altitude flight provided the greatest pull. There were lifting and pulling applications with the string paying out or pulling in; strings of varying length.
It is believed that the aim with existing aerodynamic control devices, however seldom applied, was not to control the angle-of-attack, in particular, of tethered aircraft, but rather for lifting amusements.
But the drawback was that there were no means to adjust the flight characteristics of the kites to accomodate gusting and changing winds. Many, it is thought most, of the schemes were tested long before the development of flight controls. Without control apparatus flight becomes erratic in gusting and changing winds. Flight becomes translational and rotational and sometimes crashing. Lives were lost in man lifting operations. The tractors were erratic and there were crashes, sometimes fatal.
Deflecting surfaces as used on airplanes are employed on towed gliders, and they are applied to other tethered aircraft, but they are seldom used on kites. Vanes and vents, and tails and drouges, are devices that stabilize kite flight. Kites flown with multiple tethers display dives and loops.
But, for the most part, after the development of airplanes and the myriad technological advances of this century, profitable applications of kites have declined. So that the application of feedback controls and the like to kites, tethered aircraft, has languished.
On-board apparatus for precision movement of the towing-point from one location to another location on the body is not known to be in use. Weight limitations would reduce the effectiveness of old style controls that require on-board energy sources. Because apparatus to move the towing-point during flight is currently lacking, precision control of the angle-of-attack of tethered aircraft is not accomplished.